The present invention relates to a process for producing a multilayer (or multi-ply) circuit board which is suitable for a ceramic package, multilayer boards and the like to be employed in the GHz-region requiring an especially low dielectric constant.
The Japanese Patent Kokai Publication No. 55-138899 entitled "A Process for Producing Glass Ceramic Structure", discloses the following process for producing ceramic multilayer boards using crystallized glass as an insulating material and copper as an electric conductive material, which comprises:
preparing a green laminated body by laminating a plurality of sheets each obtained by printing a pattern by using a paste containing copper as an electric conductive layer on a green sheet composed of glass particles which crystallize at a lower temperature than the melting point of copper, and injecting the copper paste into through-holes perforated beforehand at required positions of each of the green sheets;
heating the resulting laminated body at a temperature between a gradual cooling temperature and a softening temperature of the glass under a wet hydrogen atmosphere, which is oxidizing for carbon and non-oxidizing for copper, to decompose organic binders contained in the laminated body of said green sheets;
replacing the hydrogen atmosphere by an inactive atmosphere; and then
heating the laminated body to a crystallizing temperature of the glass.